The dispensing of beverages in draft form, that is as individual portions drawn off a large supply, combines the advantages of low unit cost and ease of vending with the disadvantages that it is nearly impossible to accurately monitor the liquid being dispensed. A keg of beer contains well upward of 100 glasses of beer and the vagaries of dispensing can waste substantial portions of this beer. In addition a dishonest bartender can give away beers to friends or sell beers and pocket the money with very little likelihood of detection while a careless bartender can forget to collect for beers dispensed without in any way knowing of the error.
A system is known, for instance from U.S. Pat. No. 2,330,857, for grossly measuring the contents of a keg. Such an arrangement, however does not provide information accurate enough for effective monitoring of a liquid often dispensed 6 oz or 8 oz at a time. Systems used for gas tanks and the like are seen in U.S. Pat. Nos. 2,380,249 and 4,368,640 for monitoring the level inside the tanks, but these arrangements do not apply to the dispensing of an effervescent liquid like beer where some is often lost to the foam overflow on filling.
Other arrangements are known from U.S. Pat. Nos. 2,040,357, 3,599,833, 3,665,167, and 4,202,378 for monitoring the dispensing of liquids right at the tap. These arrangements also are hard to manage and expensive and have found little use in reality. They also do not work for the dispensing of beer because the foam that is spilled out, in particular when the tap is fresh or the beer has gotten warm, is not accounted for.
Finally complicated devices have been suggested in U.S. Pat. Nos. 3,699,315 and 4,562,732 for monitoring liquids in closed vessels. These devices once again are not applicable to the dispensing of an effervescent liquid due to the losses inherently incurred even by a careful bartender in the course of his normal work.
Even the most complicated keg-tapping systems cannot account for how many beers have actually been drawn. Nor can they detect when underfilled kegs have been delivered or when the equipment has failed, as for instance when it is leaking or is allowing the beer to get too hot or cold.